Modem microelectronic packages such as flip-chip ball grid array (FCBGA) packages may include several hundred closely spaced interconnects, formed as solder joints distributed over the entire area of the integrated circuit (IC). Each interconnect includes a solder bump which connects a pad located on the IC with a corresponding pad on a substrate. Known substrates include for example printed circuit boards (PCBs) formed from organic laminates, and ceramic substrates.
Interconnects must be formed by a process that is both defect-free and reliable over the long term. A first type of defect that may be present immediately after manufacturing is an open circuit, for example due to the fact that a solder bump is too small to contact both the pad on the IC side and the pad on the substrate side. Another type of defect is a lateral short (“bridge”) between adjacent interconnects. Moreover, interconnects must be reliable over the lifetime of a product, which may be of the order of 10 years. This requires the interconnects to have a shape and structure that can withstand long-term thermal cycling without mechanical failure.
Forming defect-free and reliable interconnects between an IC and a substrate is difficult, in part because of the high variability in many critical parameters, such as the planarity of the substrate, the volume of solder bumps, IC alignment, etc. Accordingly, there is a need for a method to optimize the manufacturing of interconnects in the presence of many sources of variability.